Annotation of antisense splice sites in different subfamilies of putatively active L1s and antisense intronic FL L1 insertions. A. For illustration the polypyrimidine tracts for the site SA-154 are shown. Here, the splice donor AG motif is present only in a small fraction of full-length intact elements belonging to the A subfamily (741), whereas it is intact in GF subfamily (190). "01" marks the location of AG splice acceptor motif; "-" designates the position of the polypyrimidine tract. Exemplary Motif1 and Motif2 sequences, containing the functional SA-154 splice site, are evidenced by mapping of cDNAs (AK145348, BG144807, respectively) to the corresponding genomic locations containing L1s (NCBIm35). B. Conservation of antisense GT/AG splice motifs in potentially active L1s. C. Conservation of antisense GT/AG splice motifs in antisense intronic FL L1 insertions. "n = " indicates the number of annotated L1s/monomers. Legend: cDNA-identified splice sites.